Reuters German Chancellor Angela Merkel's spokesman says there can't be informal talks on the conditions for Britain leaving the European Union before London has filed formal notice of its intention to quit the bloc.

Only Britain can invoke Article 50 of the EU treaty, which triggers the formal process by which the country would leave the union. Departing Prime Minister David Cameron has signaled that that could take several months, while many European leaders want it to come immediately.

Merkel spokesman Steffen Seibert said Monday that "if the government needs a reasonable amount of time to do that, we respect that," but the uncertainty cannot continue forever.

Seibert said: "One thing is clear: before Great Britain has sent this notification, there will be no informal preliminary talks about the exit modalities."